The present invention relates to a system for controlling the direction of the momentum of a satellite in a geosynchronous orbit, thereby to control the attitude of the satellite.
The attitude control mechanism has the purpose of compensating the disturbance torques applied to the satellite. With a satellite having solar panels which are deployed when in orbital configuration, it is known that the main source of disturbance is the torques due to the solar pressure on the deployed solar panel arrays which are deformed such that they are not kept in perfectly symmetrical extension. In effect, the solar arrays are generally deformed due to internal stresses resulting for instance from the thermal pressure of the sun and said internal stresses cause the solar panels to be unsymmetrically deformed by tension and bending torques. An example of deformation caused by bending torque is illustrated on FIG. 1 which represents schematically a satellite S having two deployed solar panels P. One clearly notices the unsymmetrical curvature which is caused to the solar panels. The disturbing torques resulting from said unsymmetrical deformation ought to be compensated otherwise they would cause substantial drift rate of the satellite. Typical values for the drift rate are 0.02 degree/day caused by torsion torque and 0.2 degree/day caused by bending torque.
To date the attitude control mechanism usually comprises activating a suitable one of the on-board thrusters of the satellite when the roll angle reaches a predetermined threshold. Such a control mechanism requires a control loop which necessitates rather complex equipment implementation and which calls for large fuel consumption for activating the thrusters.